Media bias is when a journalist or a group of writers lean to one side, where they agree more too. People, opinions, and one really good persuasive person, are what trigger media bias. When someone forms a strong opinion on something, they will want to stick with it causing bias on their account. Then that could turn to something more and that would spread, that would be the media part.
One common and know news channels is Fox news, on channel 2. Also know about it is that it's very biased. I'm not too informed but I'm pretty sure that Fox news always lean to the side of republicans, when it comes to politics, it also shows dislike to our current president, Barack Obama, who is a democrat, the known to be opposite of republicans. It shows media bias because it obviously leans to a one sided argument for them, and they're the news where they are literally the media.